Pre-cured composite doublers may be used as patches to repair, reinforce and/or strengthen both metallic and polymer-matrix composite aircraft structures, such as outer skins. In some cases, the doublers may comprise metal that is preformed to the shape of a surface to which is to be applied. Doublers are also sometimes used to better distribute loads when added to a structure. The doublers may be bonded to the surface of the structure using a suitable adhesive in the form of one or more adhesive plies. It is normally important to achieve a good bond between the doubler and the structure across the entire area of the doubler. However, in some cases, the surface of the structure may be uneven, and/or contain one or more depressions which create a gap across the preformed doubler foot print onto the skin. The gap may be filled with sheet adhesive, but challenges may occur when the gap thickness varies. In order to assure a complete bond having maximum strength, the gaps should be filled with adhesive. Accordingly, it is necessary to determine the location and dimensions of the gaps in order to tailor the pattern of each ply of the adhesive in order to completely fill the gaps with adhesive.
Existing techniques, including manual mapping, for measuring gaps between a structure surface and a doubler are time consuming, and measurement results may depend upon the skill of the technician who makes the measurements and interprets the results. Capacitive blankets have been proposed for use in measuring the gaps, and are effective for a variety of applications. However, capacitive blankets may not be suitable for measuring gaps over large areas or surface areas that have steep or multiple contours, since the blanket may not precisely conform to all areas of the contoured surface.
Accordingly, there is a need for a method and apparatus for rapidly and reliably mapping the gaps between a doubler and the surface of a structure, especially where the surface is relatively large and/or is highly contoured. There is also a need for a method and apparatus for fabricating stacked plies of adhesive that are precisely patterned so as to completely fill all areas of the gap in order to assure a good bond between the doubler and the structural surface.